The long-term objective of the proposed research is to understand the processes underlying counterconditioning procedures. Specifically the proposed research deals with the case where a conditioned stimulus for an aversive event (CS plus AV) is followed by the appetitive unconditioned stimulus of food. The basic phenomenon of "counterconditioning" is the weakening of the conditioned response to CS plus AV produced by the above procedure. The proposed research evaluates the role of various processes which have been suggested as important in producing counterconditioning: extinction, reciprocal inhibition of responses or of central motive states, counterconditioning itself, conditioned inhibition, and effects of expectancies produced by the CS. Because the processes which have been suggested as occurring in the counterconditioning procedure are fundamental ones, understanding if and how these processes operate in the counterconditioning procedure will contribute to our understanding of learning in general. In addition, the research is of practical importance in that the highly successful behavior therapy of systematic desensitization is based on counterconditioning procedures. Understanding the processes underlying counterconditoning will aid us in increasing the efficacy of this and other behavior therapy techniques based on counterconditioning (e.g., aversion therapy).